I've been using Bittornado for several years, there was no problem at all until a few days ago, everytime I downloaded or uploaded with Bittornado, my computer got infected with trojan Vundo and trojan disabled securitycenter. Could someone tell me how to fix this problem ? thank you in advance

Vundo is transmitted via email attachments and browser exploits. You may be getting it from the torrent site you're visiting. It may also be resident and hidden on your system and is constantly reloading and redetecting.

Yes. Please contact Malwarebytes for confirmation. Some trojans use the same Windows installer as I do (http://en.wikipedia.org/wiki/Nullsoft_S ... all_System) and sometimes the viral signatures used by malware detectors use parts of the installer rather than the actual malware.